The present invention relates to capping machines for affixing plastic screw closures on glass or plastic containers for beverages or the like. More particularly it relates to the head portions of a capping machine which serve to rotate the plastic screw cap with respect to the container while pressing on the cap and applying a limited predetermined tightening torque to the cap as controlled by an internal slip clutch. The capping machine head of the present invention is characterized by a magnetic clutch for torque control, preferably in the form of concentric cylindrical configurations of about twenty to forty magnets each with their North-South magnetization oriented radially.
1. Field of the Invention
The development of capping heads has been impelled in considerable part by the changes in closures which have progressed from the traditional crowns, to roll on aluminum caps, to plastic screw caps. With the advent of plastic screw caps, it became necessary to provide the capping machine heads with a slip clutch or other means so that the rotation of the upper part of the head with the spindle after the screw cap was tightly seated would not impart excessive torque causing the cap to be over-tightened or broken. At first such clutches were typically friction slip clutches, and in more recent years, magnetic clutches or magnetic drives have been employed to control the torque applied to the screw caps.
2. Description of the Related Art
Many variations on magnetic slip clutches are known, as shown for example in Swiss Patent to N. V. Philips' Gloelampenfabricken No. 313,871, or U.K. Patent to Owens Illinois No. 2,111,964A, I.C. B67B 3/20. U.S. Pat. No. 4,492,068 to Obrist issued Jan. 8, 1985, shows the use of a magnetic slip clutch in a screw closure capping machine head which takes the form of a pair of generally identical clutch plates, each having many cylindrical magnets embedded therein in a circular pattern near the periphery of the disk. The magnets are oriented North-South alternately around the periphery, and the two plates are attracted to preferred rotational alignments where each North pole of a magnet on one phase is aligned facing the South pole of a magnet on the other plate. Adjustment of the limiting torque in such a magnetic slip clutch may be achieved by varying the space between the plates and thus increasing or decreasing the attraction or repulsion of the aligned or nearly aligned magnets of the two plates.
Another magnetic torque control drive is shown for a screw closure capping head in U.S. Pat. No. 4,485,609 to Kowal, issued Dec. 4, 1984. This patent does not employ concentric arrays of magnets however, but rather employs one array of magnets in a cylindrical configuration which is intended to cooperate with a concentric ring of material with high magnetic permeability so that torque of a limited value is imparted to the cap chuck of the head.